If no amplitude limitation is performed on a common LC oscillation circuit, an amplitude of the oscillation circuit would eventually stabilize to a power supply voltage, and such oscillation circuit has several disadvantages as follows: 1. distortion of an oscillation waveform of the oscillation circuit occurs, and a rising edge and a falling edge thereof are dissymmetrical, such that a 1/f3 noise inflection point of the oscillation circuit moves to a high frequency, resulting in worse low frequency phase noise; and 2. a large oscillation amplitude causes a very large current through an inductor, such that a magnetic core of the inductor is saturated, resulting in a change of an inductance value, ultimately affecting stability of a frequency.
Usually, an approach of limiting amplitude is to detect an oscillation amplitude by using an amplitude detection circuit or a peak detection circuit, and then output a control voltage to control a bias current of an oscillation circuit, so as to achieve an effect of limiting the amplitude of the oscillation circuit. However, the approach also has several disadvantages as follows: 1. a loop gain of such approach is larger, easily resulting in instability of a control loop; 2. the control loop per se may introduce greater noise, resulting in worse phase noise of the oscillation circuit; and 3. most of the amplitude detection circuits cannot accurately control the oscillation amplitude, thereby limiting its utility.
Therefore, it becomes a technical problem to be solved urgently to improve performance of an amplitude limiting oscillation circuit.